The Assessment of Retinal Function Using Multifocal and Full–Field Electroretinogram in a Rodent Model of Electrical Retinal Stimulus

Abstract

Abstract: : Purpose: To use the multifocal electroretinogram (mf–ERG) and full–field electroretinogram (ERG) to assess effects of electrical stimulation on the normal retina in rodent. Methods: Pigmented rats (Long Evans) were anesthetized, and an intraocular stimulating electrode was inserted into the vitreous chamber through a scleral incision near the limbus. The electrode tip (0.44cm²) touched the retina. The retina was stimulated by an external source with 1mC/cm² of electrical charge for 1 hour. After 2 weeks, animals were placed in a dark room for 2 hours and their pupils were dilated. Noninvasive monocular mf–ERGs were recorded using a contact lens electrode in a dim room. A 61–hexagon stimulus array subtending a visual angle of 45^o was projected on the fundus; its location was monitored using an infrared charge–coupled device and a fundus camera using a Visual Evoked Response Imaging System (VERIS; EDI, San Mateo, CA). Full field (Ganzfeld) ERGs were recorded using an Espion visual testing system (Diagnosys LLC, Littleton, MA) under dark–adapted conditions (12 hours) with dilation of the animals’ pupils. Unstimulated age–matched pigmented rats were used as controls. Results: In mf–ERG, the amplitudes of N1, P1 and N2 were decreased significantly compared with those of the control (p<0.05) at the location of the stimulation. There were significant delays on the implicit time of N1, P1 and N2 in the same place compared with the controls (p<0.05). Amplitudes and latencies of the scotopic and photopic full–field ERGs were not statistically different from the control eye (P>0.05). Conclusions: The mf–ERG is more useful in evaluating the focal retinal function than full–field ERG in a rodent model when the retina is electrically stimulated.

Keywords: electroretinography: non-clinical • retina • lesion study